1. Field of the Invention
This invention relates to the field of computer software and hardware. More specifically the invention relates to a method and apparatus for tracking moveable objects.
2. Background Art
Current systems provide a way to locate and track objects. For example, Automatic Vehicle Location (AVL) systems utilize the NAVSTAR Global Positioning System (GPS) to obtain data that can be used to determine the location of a vehicle. An example of a reference that further discusses GPS is the 1992 book by Tom Logsdon; "The Navstar Global Positioning System," Van Nostrand Reinhold publication, ISBN 0-442-01040-0, which is incorporated herein by reference.
Typical uses of AVL systems provide users such as trucking companies and law enforcement agencies the ability to monitor a fleet of vehicles from a home station. A typical AVL system consists of: one or more mobile units; one or more vehicle monitoring stations; and a wireless communication network. However, there are several limitations and problems associated with current AVL systems. For example, current AVL systems either track vehicles with a substantial time delay (i.e., non-real-time) or provide real-time vehicle tracking within a geographically confined boundary such as within a city. Moreover, such systems lack a mechanism for predicting movement of a vehicle while it is out of communication range with its primary communication network.
The mobile unit (MU) is a piece of hardware installed in the vehicle that is to be monitored. The MU typically contains a GPS receiver and a wireless transmitter. A problem with current MUs is that such devices are not configured to perform calculations related to processing of location information upon data obtained via the GPS receiver. For example, current MUs lack the capacity to convert raw GPS data into a minimum set of map-ready location information. The primary function of current MUs is to transmit GPS position data to a monitoring station. Typically, the MU receives positioning signals from a GPS satellite in the form of code sequences and may convert these code sequences to pseudo range information or standard GPS code (NMEA). Pseudo ranges from a minimum of four different satellites are required in most instances for position calculation. These pseudo ranges or NMEA codes are subsequently transmitted to the monitoring station, via a wireless network, for position calculation.
The vehicle monitoring station is usually computer equipment configured to process GPS data and monitor vehicle locations. These stations perform filtering of the pseudo range signals or raw GPS data transmitted from the MUs and further reduce these ranges to map coordinates for display. Current systems may also perform position corrections by using differential CPS data obtained from a station in the vicinity of the vehicle being monitored. Because of the severe computational burden placed on the computer equipment at the vehicle monitoring station, tracking a large amount of vehicles in real-time requires a substantial amount of processing power. Thus, a limitation of current systems is that such systems require the vehicle monitoring station to perform most of the calculations.
Transmitting GPS data from the vehicle to the vehicle monitoring station requires a wireless communication network. For example, current systems support transmission across cellular systems, satellite uplinks, and other forms of wireless communication. A problem with current systems is that transmission is typically limited to a single communication network. Thus, when the vehicle moves out of range of the communication network location data cannot be reported to the vehicle monitoring station. Usually, time stamped data is sent in packets from the MU to the vehicle monitoring station. Data may also be sent from the object location server to the MU, for example, when the MU desires destination information.
Several utilities derive from AVL technology including: transportation information such as traffic and road conditions, and any other geographic information; and navigation information that provides the driver with locations of destinations, directions, distance, estimated arrival time, and other necessary information. A problem with current systems is that these utilities are not always available because such AVL systems can only work at certain times and in limited locations. For example, current systems can only operate where they have access to a communication network. If, for example, the system uses a satellite, the system cannot effectively operate while a vehicle is moving through a tunnel. Moreover, such systems do not provide real-time vehicle monitoring and vehicle history tracking at all times and at any location.
Some additional problems and limitations of current systems are discussed in further detail below.
Location Data:
If a vehicle (i.e. receiver antenna) is within an obstructed view of the GPS satellites, like in a dense forest, a parking structure, or an underground tunnel, the GPS receiver cannot receive satellite signals, and no GPS data is processed. Also, there is no mechanism for determining where the vehicle traveled to while there was no link between the GPS receiver and the GPS satellite.
Wireless Communication:
If the wireless communication network employed by the AVL system is down, or if the vehicle moves outside of the network's coverage area, there will be no location data available to allow the vehicle monitoring station to determine where the vehicle went while the network was inoperative.
Real-time Access:
Even if current vehicle data is available, if the person who wants to monitor a vehicle cannot access the data, then real-time monitoring is still difficult to perform. Current systems also require that users wishing to view data showing the vehicle location download and install a mapping program in order to be able to display the vehicle location. These maps or mapping programs may have errors and result in erroneous indication of the actual vehicle location. Moreover, in corporations, public agencies, or just an Internet cafe, downloading and installing programs is cumbersome and could be prohibited for security concerns. Thus, there is a need for a system that can access vehicle location data without requiring installation of a client program that is specifically tailored for viewing vehicle location data.
In practice, current AVL technology cannot provide real-time, non-stop global vehicle tracking due to the following constraints:
There exists no single commercial or private wireless communication network that can provide a complete global coverage. Available wireless services have limited coverage areas.
No commercial or private network works all the time. There may be down times associated with available wireless services. These down times may be scheduled like for maintenance, and unscheduled like for failure related problems.
GPS data are invalid in areas not directly exposed to the GPS satellites. For GPS data to be valid, the receiver must be in unobstructed communication with a minimum of four GPS satellites.
GPS data computation, GIS data processing, and mapping are done at a data processing station. In practice, the computational loading on the data processing station is too high for current AVL system to provide a real-time vehicle monitoring for a large number of vehicles or users at the same time.